1236 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



FIG. 8. EEG tracings during 

 and after vaginal stimulation in 

 an estrogen-treated estrous rab- 

 bit. The 'after -reaction' includes 

 a sleep-like phase which here 

 lasted 7 min., and a phase of 

 'pseudo-arousal' characterized by 

 high amplitude slow waves 

 (theta rhythm) in limbic cortical 

 and hippocampal channels. Ab- 

 breviations: FC, LC, frontal 

 and limbic cortex; OB, olfactory 

 bulb; PO, preoptic area; LHA, 

 lateral hypothalamic area; VHPC 

 and DHPC, ventral and dorsal 

 hippocampus; EKG, electro- 

 cardiogram. [From Sawyer & 

 Kawakami, unpul^lishcd olxser- 

 vations.l 





EKG i- 



k.V#''''ar'#fcW/.T.'//W^~ 



STIM 

 4 MIN 



'■VV'V'^/W- 





7 MIN 



has reported heightened EEG acthity in tlie anterior 

 hypothalamus during courtsliip and mating pro- 

 cedures. In similarly prepared rabbits, Kawakami 

 and Sawyer have recently observed a generalized 

 EEG 'after-reaction' which includes several minutes 

 of a sleep-like record followed by an unusually 

 aroused pattern. We have suggested that the latter is 

 'pseudo-arousal' since the rabbit remains quiescent 

 while an extreme degree of EEG arousal is being 

 registered. The response can also be evoked by 

 vaginal stimulation in the estrogen-primed or estrogen- 

 progesterone-treated rabbit (fig. 8). More interest- 

 ingly, from the viewpoint of hypothalamic function, 

 the 'after-reaction' EEG sequence can be initiated by 

 low-frequency electrical stimulation, applied directly 

 to the ventromedial region of the hypothalamus. 

 Thresholds of this reaction will be mentioned below. 

 Further evidence for central sites of sex hormone 

 action on behavior comes from the results of injecting 

 hormone preparations directly into the cerebral 

 ventricles or the brain tissue itself Kent & Liberman 

 (50) were able to induce psychic estrus in the castrate 



estrogen-primed hamster by injecting into the lateral 

 ventricles of the brain a dose of progesterone too 

 small to be effective via the systemic route. Harris 

 (45) attempted to produce tnating beha\ior in 

 ovariectomized rabbits bv injecting small amounts of 

 stilbestrol into the hypothalamus — only to find that 

 some of his untreated controls would mate without 

 estrogen. He has more recently repeated this experi- 

 ment with the female cat, and he reports that hy- 

 pothalamically injected estrogen in doses too small to 

 affect the uterus does indeed evoke psychic estrus 

 (46). Fisher (30) reported the induction of sexual and 

 maternal behavioral patterns in male rats by the in- 

 jection of testosterone into the preoptic region. 



An avenue of approach to the cerebral localization 

 of sex drive is the self-stimulation technique of Olds & 

 Milner (66). Rats with electrodes implanted in \ari- 

 ous regions of the brain are permitted to stimulate 

 themselves ad libitum by pressing a bar in a Skinner 

 box. Many areas are positively reinforcing; the elec- 

 trical stimulus 'reward' activates repeated bar press- 

 ing at a rate dependent on the region and the strength 



